const SNOW = function(width, height, center, toRandomize){
    this.width = width;
    this.height = height;
    this.center = center;
    this.init(toRandomize);
};
const RENDERER = {
    SNOW_COUNT: {INIT: 100, DELTA: 1},
    BACKGROUND_COLOR: 'hsl(%h, 50%, %l%)',
    INIT_HUE: 180,
    DELTA_HUE: 0.1,

    init: function () {
        this.setParameters();
        this.reconstructMethod();
        this.createSnow(this.SNOW_COUNT.INIT * this.countRate, true);
        this.render();
    },
    setParameters: function () {
        this.$container = $('#snow-container');
        this.width = this.$container.width();
        this.height = this.$container.height();
        this.center = {x: this.width / 2, y: this.height / 2};
        this.countRate = this.width * this.height / 500 / 500;
        this.canvas = $('<canvas />').attr({width: this.width, height: this.height}).appendTo(this.$container).get(0);
        this.context = this.canvas.getContext('2d');

        this.radius = Math.sqrt(this.center.x * this.center.x + this.center.y * this.center.y);
        this.hue = this.INIT_HUE;
        this.snows = [];
    },
    reconstructMethod: function () {
        this.render = this.render.bind(this);
    },
    createSnow: function (count, toRandomize) {
        for (let i = 0; i < count; i++) {
            this.snows.push(new SNOW(this.width, this.height, this.center, toRandomize));
        }
    },
    render: function () {
        requestAnimationFrame(this.render);

        const gradient = this.context.createRadialGradient(this.center.x, this.center.y, 0, this.center.x, this.center.y, this.radius),
            backgroundColor = this.BACKGROUND_COLOR.replace('%h', this.hue);

        gradient.addColorStop(0, backgroundColor.replace('%l', 30));
        gradient.addColorStop(0.2, backgroundColor.replace('%l', 20));
        gradient.addColorStop(1, backgroundColor.replace('%l', 5));

        this.context.fillStyle = gradient;
        this.context.fillRect(0, 0, this.width, this.height);

        for (let i = this.snows.length - 1; i >= 0; i--) {
            if (!this.snows[i].render(this.context)) {
                this.snows.splice(i, 1);
            }
        }
        this.hue += this.DELTA_HUE;
        this.hue %= 360;

        this.createSnow(this.SNOW_COUNT.DELTA, false);
    }
};
SNOW.prototype = {
    RADIUS : 20,
    OFFSET : 4,
    INIT_POSITION_MARGIN : 20,
    COLOR : 'rgba(255, 255, 255, 0.8)',
    TOP_RADIUS : {MIN : 1, MAX : 3},
    SCALE : {INIT : 0.04, DELTA : 0.01},
    DELTA_ROTATE : {MIN : -Math.PI / 180 / 2, MAX : Math.PI / 180 / 2},
    THRESHOLD_TRANSPARENCY : 0.7,
    VELOCITY : {MIN : -1, MAX : 1},
    LINE_WIDTH : 2,
    BLUR : 10,

    init : function(toRandomize){
        this.setParameters(toRandomize);
        this.createSnow();
    },
    setParameters : function(toRandomize){
        if(!this.canvas){
            this.radius = this.RADIUS + this.TOP_RADIUS.MAX * 2 + this.LINE_WIDTH;
            this.length = this.radius * 2;
            this.canvas = $('<canvas />').attr({width : this.length, height : this.length}).get(0);
            this.context = this.canvas.getContext('2d');
        }
        this.topRadius = this.getRandomValue(this.TOP_RADIUS);

        const theta = Math.PI * 2 * Math.random();

        this.x = this.center.x + this.INIT_POSITION_MARGIN * Math.cos(theta);
        this.y = this.center.y + this.INIT_POSITION_MARGIN * Math.sin(theta);
        this.vx = this.getRandomValue(this.VELOCITY);
        this.vy = this.getRandomValue(this.VELOCITY);

        this.deltaRotate = this.getRandomValue(this.DELTA_ROTATE);
        this.scale = this.SCALE.INIT;
        this.deltaScale = 1 + this.SCALE.DELTA * 500 / Math.max(this.width, this.height);
        this.rotate = 0;

        if(toRandomize){
            let i = 0, count = Math.random() * 1000;
            for(; i < count; i++){
                this.x += this.vx;
                this.y += this.vy;
                this.scale *= this.deltaScale;
                this.rotate += this.deltaRotate;
            }
        }
    },
    getRandomValue : function(range){
        return range.MIN + (range.MAX - range.MIN) * Math.random();
    },
    createSnow : function(){
        let y;
        this.context.clearRect(0, 0, this.length, this.length);

        this.context.save();
        this.context.beginPath();
        this.context.translate(this.radius, this.radius);
        this.context.strokeStyle = this.COLOR;
        this.context.lineWidth = this.LINE_WIDTH;
        this.context.shadowColor = this.COLOR;
        this.context.shadowBlur = this.BLUR;

        const angle60 = Math.PI / 180 * 60,
            sin60 = Math.sin(angle60),
            cos60 = Math.cos(angle60),
            threshold = Math.random() * this.RADIUS / this.OFFSET | 0,
            rate = 0.5 + Math.random() * 0.5,
            offsetY = this.OFFSET * Math.random() * 2,
            offsetCount = this.RADIUS / this.OFFSET;

        for(let i = 0; i < 6; i++){
            let j;
            this.context.save();
            this.context.rotate(angle60 * i);

            for(j = 0; j <= threshold; j++){
                y = -this.OFFSET * j;

                this.context.moveTo(0, y);
                this.context.lineTo(y * sin60, y * cos60);
            }
            for(j = threshold; j < offsetCount; j++){
                y = -this.OFFSET * j;
                const x = j * (offsetCount - j + 1) * rate;

                this.context.moveTo(x, y - offsetY);
                this.context.lineTo(0, y);
                this.context.lineTo(-x, y - offsetY);
            }
            this.context.moveTo(0, 0);
            this.context.lineTo(0, -this.RADIUS);
            this.context.arc(0, -this.RADIUS - this.topRadius, this.topRadius, Math.PI / 2, Math.PI * 2.5, false);
            this.context.restore();
        }
        this.context.stroke();
        this.context.restore();
    },
    render : function(context){
        context.save();

        if(this.scale > this.THRESHOLD_TRANSPARENCY){
            context.globalAlpha = Math.max(0, (1 - this.scale) / (1 - this.THRESHOLD_TRANSPARENCY));

            if(this.scale > 1 || this.x < -this.radius || this.x > this.width + this.radius || this.y < -this.radius || this.y > this.height + this.radius){
                context.restore();
                return false;
            }
        }
        context.translate(this.x, this.y);
        context.rotate(this.rotate);
        context.scale(this.scale, this.scale);
        context.drawImage(this.canvas, -this.radius, -this.radius);
        context.restore();

        this.x += this.vx;
        this.y += this.vy;
        this.scale *= this.deltaScale;
        this.rotate += this.deltaRotate;
        return true;
    }
};

$(function(){
    RENDERER.init();
});
